I am having issues with the pivot constraint
It is a Loop Dependency. You can't make a children object parent father of is father.
A constraint look like a parent in Blender, so you have to make some parents organization in your file.

Arm Rotation is Father of Shovel.
But, Arm Rotation is in the Pivot constraint of Shovel, so, it's child of Shovel.

This parenting are avoid, you have to use bones and armature to simplify.